The present invention relates to a process for producing hydrogen by algae in an alternating light/dark cycle.
Hydrogen is one of the noteworthy clean energy sources which will be able to take the place of fossil fuel such as petroleum and coal. Hydrogen has various advantages as an energy source such that (1) it can be converted to electric energy effectively by means of a fuel cell, (2) its calorie per unit weight is 3 to 4 times of that of petroleum, and it burns to form only water so that it does not pollute the environment, and (3) water, which is one of the raw materials for producing hydrogen, is inexhaustible.
The processes for the production of hydrogen by means of solar energy are classified into two classes, one of which is a non-biological process using semiconductors and the other of which is a biological process using photosynthetic products. With respect to the latter biological process, there proposed some systems for biophotolyzing water to produce hydrogen by controlling the metabolism of higher plants and algae having the ability to decompose water or by combining said higher plants and algae with a microorganism having the ability to decompose water. However, in conventional systems, oxygen produced by photolysis of water deactivates or prohibits the activity of the hydrogen producing system (i.e. hydrogenase), which results in unstability in the production of hydrogen. Further, isolation and purification of hydrogen is difficult, and there is a possibility of explosion of a gaseous mixture of oxygen and hydrogen. Therefore, the conventional systems are not practical.